Hydrocephalus is defined as a clinical entity in which a disturbance of cerebrospinal fluid (CSF) circulation causes the accumulation of intraventricular CSF, resulting in progressive ventricular dilation. It can be divided as two groups: hydrocephalus seen in early life and hydrocephalus seen in adults based on the time of onset. In the early life hydrocephalus group, fetal hydrocephalus is of significant concern since children with an obvious prenatal onset of hydrocephalus have been found to be at high risk for early death or multiple neurological impairments. It is reported that fetal hydrocephalus occurs at an estimated rate of 0.2-1 per 1,000 deliveries and the prevalence varies due to the various or obscure definitions of congenital hydrocephalus. Fetal pressure hydrocephalus due to obstruction of flow of fluid through and then out of the ventricular system damages the developing brain. Neurologic consequences are devastating and permanent.
Aqueductal stenosis (AS) is a unique neurodevelopmental anomaly that causes pressure hydrocephalus by obstruction of the aqueduct of Sylvius, which is the narrowest portion of the central nervous system (CNS) ventricular system between the third and fourth ventricles. It is fundamentally different from other causes of hydrocephalus that result from a malformation, deformation, or disruption of the developing brain. Fetuses with AS, usually have otherwise normal brains. Neurologic injury in AS is the result of pressure on the developing neurons. It therefore stands to reason that fetuses with AS may benefit from decompression of the ventricular system, thereby arresting brain injury and preventing ongoing damage.
In-utero shunting of CSF from the ventricles to the amniotic fluid was attempted in the early 1980s as a means of improving pregnancy outcomes. The ventriculoamniotic shunts were, in general, simple silastic tubes with a one-way valve to prevent amniotic fluid from refluxing into the ventricles. They were placed by ultrasound guidance through a large bore needle. They had a tendency to clog. In addition, they had a tendency to migrate since there was no effective means for anchoring the device to prevent dislodgement. Intrauterine treatment was shown to be technically feasible. Shunting was abandoned, however, in the mid-1980s due to a perceived lack of effect. In retrospect, the lack of effect was likely due to poor patient selection and technical difficulties as a consequence of technological limitations of the day. Because of the inability to accurately assess fetal neuroanatomy in the 1980s, shunts were placed in fetuses with lesions other than AS. Not surprisingly, analysis of the data on pregnancy outcomes after shunting showed no clear benefit. A moratorium was placed on fetal ventriculoamniotic shunting in the mid-1980s and since, there has been almost no progress in treatment of fetal hydrocephalus and ventriculoamniotic shunts are not commercially available.
Prenatal ventricular decompression is currently not a management option for fetal pressure hydrocephalus. Current management for fetal hydrocephalus involves either preterm delivery followed by postnatal shunting or expectant management to term and then shunting. Problems associated with early delivery are concomitant prematurity, poor surgical candidacy, and a greater rate of shunt complications. Problems associated with expectant management are ongoing brain injury and obstetric complications related to macrocephaly (excessively large fetal head), which can impact the current as well as future pregnancies due to the need for cesarean delivery. The type of cesarean section typically required is a “classical,” or vertical uterine incision which is subject to rupture in subsequent pregnancies, placing both mother and fetus at risk for death or disability. This represents an unfavorable risk-benefit assessment as the mother is exposed to significant risk, but the newborn may not receive benefit since neurologic damage is typically complete by term.
Thus, there is a need to address these issues by identifying an appropriate patient population for ventriculoamniotic shunting, i.e., isolated AS, through prenatal detection devices and methods including ultrasound and MRI techniques and, designing and developing in-utero shunting devices and methods for arresting brain injury and allowing the pregnancy to proceed to term, after which standard ventriculoperitoneal shunting can be performed in the newborn period. Neurologic function is potentially preserved while the pregnancy progresses to term. Term newborns are superior surgical candidates as compared to preterm infants.